Shielding is used in a variety of cables to reduce electrical interference that could affect a signal travelling through the cable. The shielding also helps to prevent the signal from radiating from the cable and interfering with other devices. One such type of shielding includes either one or two layers of aluminum or other shielding material (such as silver, copper, or Mu-metal) wherein each shielding layer is laminated onto (and if there is more than one shielding layer, each shielding layer is separated by) a separating layer, such as a plastic, e.g., polyethylene terephthalate (“PET”) or a polyolefin such as polypropylene (“PP”). This type of shielding that combines layers of shielding material and separating layers is often referred to as either “foil,” “laminated tape,” “shielding tape,” “shielding laminate tape,” and combinations or variations thereof.
In some cables, such as coaxial cables, multiple layers of shielding tape (each of which has either one shielding layer or two shielding layers) are employed in the cable. For example, “tri-shield” cable includes an inner foil surrounded by a braid, which is in turn surrounded by an outer foil. “Quad-shield” cable includes an inner foil surrounded by an inner braid, which is in turn surrounded by an outer foil, in turn surrounded by an outer braid.
Multiple layers of shielding tape, while providing better shielding performance, also add to the cost and complexity of producing the cabling. Conventional shielding tape, with only one or two shielding layers, is susceptible to allowing RF signal egress or ingress as micro-cracks form in the shielding layers and align with each other as a result of flexing the cable. Furthermore, the outer shielding structures (such as tape) of conventional cables must often be removed in order to attach a connector. These outer shielding structures may also separate and interfere with the attachment of a connector to the cable.
The present invention overcomes these and other problems associated with conventional shielding tape and cable designs. In particular, by using shielding tape of the present invention (that incorporates three or more shielding layers) as the inner foil of a cable, outer shielding structures (such as shielding tape and/or braids) can be eliminated. This not only reduces the cost of the cable, but obviates the need for these outer shielding structures to be removed to attach a connector to the cable. Likewise, by including additional shielding layers to the inner shielding tape, the present invention eliminates the potential problem of the outer shielding structures separating and interfering with connector attachment. Furthermore, the use of three or more shielding layers in the shielding tape of the present invention improves the flex life of the shield tape by covering micro-cracks in the metal layers with additional shielding layers, thus reducing signal egress or ingress.